Auflistung nach Autor:in "Fierz-Schmidhauser, Rahel"

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Effects of relative humidity on aerosol light scattering. results from different European sites
(Copernicus, 2013) Zieger, Paul; Fierz-Schmidhauser, Rahel; Weingartner, Ernest; Baltensperger, Urs
The effect of aerosol water uptake on the aerosol particle light scattering coefficient (σsp) is described in this study by comparing measurements from five European sites: the Jungfraujoch, located in the Swiss Alps at 3580 m a.s.l.; Ny-Ålesund, located on Spitsbergen in the Arctic; Mace Head, a coastal site in Ireland; Cabauw, a rural site in the Netherlands; and Melpitz, a regional background site in Eastern Germany. These sites were selected according to the aerosol type usually encountered at that location. The scattering enhancement factor f(RH, λ) is the key parameter to describe the effect of water uptake on the particle light scattering. It is defined as the σsp(RH) at a certain relative humidity (RH) and wavelength λ divided by its dry value. f(RH) at the five sites varied widely, starting at very low values of f(RH = 85%, λ = 550 nm) around 1.28 for mineral dust, and reaching up to 3.41 for Arctic aerosol. Hysteresis behavior was observed at all sites except at the Jungfraujoch (due to the absence of sea salt). Closure studies and Mie simulations showed that both size and chemical composition determine the magnitude of f(RH). Both parameters are also needed to successfully predict f(RH). Finally, the measurement results were compared to the widely used aerosol model, OPAC (Hess et al., 1998). Significant discrepancies were seen, especially at intermediate RH ranges; these were mainly attributed to inappropriate implementation of hygroscopic growth in the OPAC model. Replacement of the hygroscopic growth with values from the recent literature resulted in a clear improvement of the OPAC model.
01A - Beitrag in wissenschaftlicher Zeitschrift
Influence of water uptake on the aerosol particle light scattering coefficients of the Central European aerosol
(Stockholm University Press, 2014) Zieger, Paul; Fierz-Schmidhauser, Rahel; Poulain, Laurent; Müller, Thomas; Birmili, Wolfram; Spindler, Gerald; Wiedensohler, Alfred; Baltensperger, Urs; Weingartner, Ernest
01A - Beitrag in wissenschaftlicher Zeitschrift
Measured and predicted aerosol light scattering enhancement factors at the high alpine site Jungfraujoch
(Copernicus, 05.03.2010) Fierz-Schmidhauser, Rahel; Zieger, Paul; Gysel, Martin; Kammermann, Lukas; DeCarlo, Peter F.; Baltensperger, Urs; Weingartner, Ernest
Ambient relative humidity (RH) determines the water content of atmospheric aerosol particles and thus has an important influence on the amount of visible light scattered by particles. The RH dependence of the particle light scattering coefficient (σsp) is therefore an important variable for climate forcing calculations. We used a humidification system for a nephelometer which allows for the measurement of σsp at a defined RH in the range of 20–95%. In this paper we present measurements of light scattering enhancement factors f(RH)=σsp(RH)/σsp(dry) from a 1-month campaign (May 2008) at the high alpine site Jungfraujoch (3580 m a.s.l.), Switzerland. Measurements at the Jungfraujoch are representative for the lower free troposphere above Central Europe. For this aerosol type hardly any information about the f(RH) is available so far. At this site, f(RH=85%) varied between 1.2 and 3.3. Measured f(RH) agreed well with f(RH) calculated with Mie theory using measurements of the size distribution, chemical composition and hygroscopic diameter growth factors as input. Good f(RH) predictions at RH<85% were also obtained with a simplified model, which uses the Ångström exponent of σsp(dry) as input. RH influences further intensive optical aerosol properties. The backscatter fraction decreased by about 30% from 0.128 to 0.089, and the single scattering albedo increased on average by 0.05 at 85% RH compared to dry conditions. These changes in σsp, backscatter fraction and single scattering albedo have a distinct impact on the radiative forcing of the Jungfraujoch aerosol.
01A - Beitrag in wissenschaftlicher Zeitschrift
Measurement of relative humidity dependent light scattering of aerosols
(Copernicus, 21.01.2010) Fierz-Schmidhauser, Rahel; Zieger, Paul; Wehrle, Günther; Jefferson, Anne; Ogren, John A.; Baltensperger, Urs; Weingartner, Ernest
Relative humidity (RH) influences the water content of aerosol particles and therefore has an important impact on the particles' ability to scatter visible light. The RH dependence of the particle light scattering coefficient (σsp is therefore an important measure for climate forcing calculations. We built a humidification system for a nephelometer which allows the measurement of σsp at a defined RH in the range of 40–90%. This RH conditioner consists of a humidifier followed by a dryer, which enables us to measure the hysteresis behavior of deliquescent aerosol particles. In this paper we present the set-up of a new humidified nephelometer, a detailed characterization with well defined laboratory generated aerosols, and a first application in the field by comparing our instrument to another humidified nephelometer. Monodisperse ammonium sulfate and sodium chloride particles were measured at four different dry particle sizes. Agreement between measurement and prediction based on Mie theory was found for both σsp and f(RH)=σsp(RH)/σsp(dry) within the range of uncertainty. The two humidified nephelometers measuring at a rural site in the Black Forest (Germany) often detected different f(RH), probably caused by the aerosol hysteresis behavior: when the aerosol was metastable, therefore was scattering more light, only one instrument detected the higher f(RH).
01A - Beitrag in wissenschaftlicher Zeitschrift
Minimizing light absorption measurement artifacts of the Aethalometer. evaluation of five correction algorithms
(Copernicus, 13.04.2010) Collaud Coen, Martine; Weingartner, Ernest; Apituley, Arnaud; Ceburnis, Darius; Fierz-Schmidhauser, Rahel; Flentje, Harald; Henzing, J.S.; Jennings, Stephen G.; Moerman, Marcel; Petzold, Andreas; Schmid, Otmar; Baltensperger, Urs
The aerosol light absorption coefficient is an essential parameter involved in atmospheric radiation budget calculations. The Aethalometer (AE) has the great advantage of measuring the aerosol light absorption coefficient at several wavelengths, but the derived absorption coefficients are systematically too high when compared to reference methods. Up to now, four different correction algorithms of the AE absorption coefficients have been proposed by several authors. A new correction scheme based on these previously published methods has been developed, which accounts for the optical properties of the aerosol particles embedded in the filter. All the corrections have been tested on six datasets representing different aerosol types and loadings and include multi-wavelength AE and white-light AE. All the corrections have also been evaluated through comparison with a Multi-Angle Absorption Photometer (MAAP) for four datasets lasting between 6 months and five years. The modification of the wavelength dependence by the different corrections is analyzed in detail. The performances and the limits of all AE corrections are determined and recommendations are given.
01A - Beitrag in wissenschaftlicher Zeitschrift
Mobility particle size spectrometers. harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions
(Copernicus, 29.03.2012) Wiedensohler, Alfred; Birmili, Wolfram; Nowak, Marta; Sonntag, André; Weinhold, Kay; Merkel, Maik; Wehner, Birgit; Tuch, Thomas; Pfeifer, Sascha; Fiebig, Markus; Fjäraa, Ann Mari; Asmi, Eija; Sellegri, Karine; Depuy, R.; Venzac, Hervé; Villani, Paolo; Laj, Paolo; Aalto, Pasi Pekka; Ogren, John A.; Swietlicki, Erik; Williams, Paul I.; Roldin, Pontus; Quincey, Paul; Hüglin, Christoph; Fierz-Schmidhauser, Rahel; Gysel, Martin; Weingartner, Ernest; Riccobono, Francesco; Santos, S.; Gruening, Carsten; Faloon, K.; Beddows, D.; Harrison, Roy; Monahan, C.; Jennings, Stephen G.; O'Dowd, Colin D.; Marinoni, Angela; Horn, H.-G.; Keck, L.; Jiang, Jingkun; Scheckman, Jakob; McMurry, Peter H.; Deng, Zhaoze; Zhao, Chunsheng; Moerman, Marcel; Henzing, Bas; de Leeuw, Gerrit; Löschau, G.; Bastian, S.
Abstract. Mobility particle size spectrometers often referred to as DMPS (Differential Mobility Particle Sizers) or SMPS (Scanning Mobility Particle Sizers) have found a wide range of applications in atmospheric aerosol research. However, comparability of measurements conducted world-wide is hampered by lack of generally accepted technical standards and guidelines with respect to the instrumental set-up, measurement mode, data evaluation as well as quality control. Technical standards were developed for a minimum requirement of mobility size spectrometry to perform long-term atmospheric aerosol measurements. Technical recommendations include continuous monitoring of flow rates, temperature, pressure, and relative humidity for the sheath and sample air in the differential mobility analyzer. We compared commercial and custom-made inversion routines to calculate the particle number size distributions from the measured electrical mobility distribution. All inversion routines are comparable within few per cent uncertainty for a given set of raw data. Furthermore, this work summarizes the results from several instrument intercomparison workshops conducted within the European infrastructure project EUSAAR (European Supersites for Atmospheric Aerosol Research) and ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network) to determine present uncertainties especially of custom-built mobility particle size spectrometers. Under controlled laboratory conditions, the particle number size distributions from 20 to 200 nm determined by mobility particle size spectrometers of different design are within an uncertainty range of around ±10% after correcting internal particle losses, while below and above this size range the discrepancies increased. For particles larger than 200 nm, the uncertainty range increased to 30%, which could not be explained. The network reference mobility spectrometers with identical design agreed within ±4% in the peak particle number concentration when all settings were done carefully. The consistency of these reference instruments to the total particle number concentration was demonstrated to be less than 5%. Additionally, a new data structure for particle number size distributions was introduced to store and disseminate the data at EMEP (European Monitoring and Evaluation Program). This structure contains three levels: raw data, processed data, and final particle size distributions. Importantly, we recommend reporting raw measurements including all relevant instrument parameters as well as a complete documentation on all data transformation and correction steps. These technical and data structure standards aim to enhance the quality of long-term size distribution measurements, their comparability between different networks and sites, and their transparency and traceability back to raw data.
01A - Beitrag in wissenschaftlicher Zeitschrift